United States Patent Application Publication No. 2008/0106830 A1 discloses an induction channel furnace with a melt to bushing current detector. Melt in the loop is intentionally ungrounded and must be at an above ground potential for the detector to operate. A wire conductor connects the electrically conductive bushing to a ground current detector. The current detector depends upon the potential differential between the melt in the loop and ground potential so that when melt penetrates the refractory and comes in contact with the electrically conductive bushing, a current flow is established between the bushing (now at the above ground potential of the melt in the loop) and electrical ground. The magnitude of ground circuit current can be monitored and used to disconnect power to the furnace coil when the melt penetrates the refractory and comes in contact with the bushing.
U.S. Pat. No. 6,208,682 B1 discloses an induction channel furnace without a cooling jacket (bushing). The furnace utilizes two fire (or detection) walls 21 and 22 to ensure that melt from the loop does not penetrate through refractory to the furnace coil. Wall 21 is farther away from the coil than wall 22. First fire wall 21 is cylindrical and coaxially arranged around the furnace coil. The first fire wall is formed from an open electrically conductive material (metallic net or mesh) that is backed on both sides with mica insulation. The second fire wall 22 is similarly formed as the first fire wall and optionally of heavier gauge wire than the first fire wall to reinforce the refractory. Measuring the resistance between the first and second fire wall is also disclosed.
It is one object of the present invention to provide for detection of melt adjacent to the bushing in an induction channel furnace while keeping the melt in the loop at ground potential and without utilizing an electromagnetically induced voltage for the detection circuit.